Strong fibrous sheet material and method of making the same



United States Patent Int. Cl. B32b 27/06 US. Cl. 161-53 Claims ABSTRACTOF THE DISCLOSURE A strong fibrous sheet is formed by assembling aprimary mat of intermeshed fibers with a second mat of intermeshedfibers, penetrating the thickness of both of the mats with an aqueoussuspension of distinct, swollen collagen fibers of microscopic size andremoving the swelling water from the collagen to reaggregate thecollagen fibers into a larger collagen fiber structure holding theprimary mat and second mat of fibers firmly together and reinforcing theintermeshed fibers in each of the mats against displacement. The secondmat may be either woven or nonwoven and provides a fiber structureresisting lengthwise and widthwise forces and providing superior surfacecharacter.

This invention relates to an improvement in strong fibrous sheetmaterial and to a method of making the same.

In the co-pending application of Shu-Tung Tu, Ser. No. 356,067, filedMar 31, 1964, now US. Patent 3,362,- 849, entitled Manufacture of StrongFibrous Material there is disclosed the manufacture of a leather-likematerial in which lightly tanned collagen suspended in an aqueous mediumas distinct, slightly swollen fibers of microscopic size is caused topenetrate an intermeshed fibrous mass, Thereafter, by altering theconditions the fibers are deswelled and associated with each other as alarger collagen fiber structure extending through the fibrous mass andassociated with the fibers of the mass to reinforce them againstdisplacement. The reinforced fiber masses so produced are strong andpossess many of the characteristics of leather. However, it has beenfound that unless special precautions are observed, an undesirablesurface character may develop in a finished surface of such a fibrousmass when the mass is subjected to stretching.

It is an object of the present invention to provide an improvedleather-like sheet material possessing superior surface characteristicsand a novel method of making same.

To these ends and in accordance with a feature of the present invention,a special fiber relation is provided at at least one surface of theintermeshed fiber mat, and a suspension of slightly swollen collagenfibers is caused to penetrate the inter-fiber spaces of the intermeshedfiber mat. It is found that on altering the conditions to desWell thefibers and associate them as a larger collagen fiber structure, theintermeshed fibers are firmly held as a unitary strong sheet.

In accordance with a further feature of the invention the special fiberrelation at the surface of the mat is provided by disposing a separatemat or layer of intermeshed fibers on a surface of the primary mat andpenetrating interfiber spaces with collagen fiber. It is found that thecollagen fiber structure extending through both mats is effective tohold the mats firmly together so that the special characteristics of onecooperate with and aug- 3,440,131 Patented Apr. 22, 1969 "ice ment theproperties of the other intermeshed fiber mat.

Superior surface character is obtained according to the present.invention by providing fibers, preferably fine denier fibers, at leastat and adjacent one surface of the intermeshed fiber mat extendingsubstantially parallel to the surface and oriented to resist lengthwiseand widthwise forces exerted on the mat. Needling, commonly employed togive dimensional stability and delamination resistance to mats ofnonwoven fibers, disrupts the surfaceparallel relation of the fibers andit has been found important that the surface fibers be in unneedled, orat most very lightly needled relation. This relation can be used in thepresent situation because of the desirable fiber holding action of thecollagen structure formed in the mat which resists delamination.

Intermeshed fiber mats which can be employed include single unneedled orvery lightly needled mats which may be laid down by carding, air layingor otherwise depositing fibers in essentially surface parallel relation.Preferably, however, two or more mats are laid up in face to facerelation. This provides greater flexibility and convenience inoperation. The primary or base mat may be of different character fromthe fiber layer forming the surface and difiiculties arising where themat is needled are in large measure compensated for by an unneedledfiber layer forming the surface.

The intermeshed fiber mats, usually in sheet form may be selected from awide variety of woven or nonwoven fibrous materials. Ordinarily, anonwoven fiber mat is preferred for the first or base layer ofintermeshed fiber because of the great variety of thicknesses, densitiesand openness to penetration by collagen fiber suspensions which areobtainable in such nonwoven mats. These mats may be composed of variousfibers or mixtures of fibers, usually textile fibers, including nylon,polyacrylic ester fibers (Orlon), polyester fibers (Dacron),polypropylene fibers, wool, extruded cellulosic fibers such as viscoseor cellulose acetate and others. For special purposes, a mat of longercollagen fibrous material which has been treated, for example by chrometanning or other treatment to decrease its affinity for water may beused. Cotton fiber mats, preferably treated to decrease the affinity ofthe cotton for water are also usable. As discussed at greater length inthe copending application above-referred to the intermeshed fibermaterial used in the first or base layer may have relatively largeinterstitial spaces between fibers. Optionally, the fibers in the matmay be in the relation produced by needling in which fibers are forcedin a direction transverse to the plane of the mat to improve resistanceto delamination.

Unneedled fiber mats, particularly mats of crimped fibers appear tooffer special advantages as a first or base layer of mat. The mat takesup collagen fiber from suspension with great uniformity because of theabsence of the irregularities created by needling; and crimped fibersresist excessive compaction of the mat by the pressure of the collagenfiber suspension being forced into the mat. Also it appears that thecrimped fiber has a more effective collagen fiber entrapping action thanuncrimped fiber so that a high collagen content product is obtained.Also the collagen fiber entrapped in such a mat has a superiormechanical locking action on the crimped fiber so that the product hasgreater integrity. It appears that a rate of crimping corresponding toat least about 5 crimps per inch is elfective to give this result andhigher crimped fiber is useful.

Without regard to whether the mat is crimped or uncrimped fiber, it isnoted that because of its water content, the volume occupied by collagenfiber after removal of the water is much less than occupied by thepenetrating fiber suspension so that in the relatively large openingscreated in a needled mat by the action of the needles, there is atendency for development of fiber poor or fiberfree spaces within theneedle craters after removal of water, while the unneedled fiber mat isfree from such void spaces. A still further advantage is that since in aneedled mat fibers are displaced in a direction normal to the mat by theaction of the needles and these displaced fibers resist compression ofthe mat, when a needled mat is dried with resultant loss in volume ofthe collagen, the mat cannot be compacted in the areas surrounding theneedle holes and further voids develop.

Satisfactory fiber density and relation have been found in nylon fibermats having densities of the order of 4 oz. per sq. yd. at a thicknessof 0.15" and 6 oz. per sq. yd. at a thickness of 0.175". Another highlysatisfactory mate-rial is a polypropylene fiber mat having densities of7 oz. per sq. yd. and a thickness of 0.2". It is preferred that thefibers be relatively fine, e.g. in the range of from 1 to denier with 3denier being satisfactory.

The second intermeshed fiber layer may be a woven or nonwoven sheet. Thefibers in this layer may be up to 5 denier, but for best surfaceappearance it is preferred to use finer denier, suitably 0.5 to 3denier, than the fibers in the base layer. Because of the high strengthavailable with minimum thickness it is often desirable that this layerbe composed of continuous threads either of twisted staple fibers ormonofilaments with threads disposed in line with expected stresses to beapplied to the finished material. A simple weave comparable to the weaveof a batiste fabric providing threads extending at right angles to eachother has proved satisfactory. However, a comparable result can beobtained using a sheet of fibers lying generally parallel to the facesof the sheet and oriented to provide strength both lengthwise andwidthwise of the sheet as in random orientation or with one set or layerof fibers, e.g. a carded layer extending in one direction and anotherset or layer of fibers extending in a direction, suitably 90 away fromthe direction of the first set or layer of fibers.

Although the fine woven fabric offers a high degree of strength with aminimum thickness, special advantages are also obtainable through theuse as a second layer of a nonwoven, preferably unneedled mat, suitablyof different fibers from the first or base mat. Thus, as indicatedabove, the second layer may be composed of fibers of finer denier suchas 0.5 to 3.0, or the fibers may be of a material cooperating moreeffectively with a finish to be applied to the final sheet. For example,nylon fibers may be more compatible with various finishes than would,for example polypropylene fibers where the base is composed ofpolypropylene fibers.

It has been found that simply associating the base mat with a secondlayer of intermeshed fibers is all that is required and it is notnecessary that adhesives or mechanical fastening such as a needlingtreatment be used to secure the base sheet and second sheet together.Also more than two layers of intermeshed fibers may be assembled in faceto face relationship and the layer of fibers lying generally parallel tothe faces of the sheet may be a layer other than one of the surfacelayers.

The suspension if microscopic lightly tanned collagen fibers used in thepresent process may be that described in greater detail in theapplication of Tu referred to above. Briefly, the suspension is preparedby beating in water the collagen source, for example skin or hide, underconditions which limit swelling of the collagen to reduce it to fibersof microscopic size suspended in the water in a manner allowing thefibers relatively free movement in the suspension. The condition ismarkedly different from that referred to as colloidal in which collagenis reduced to a swollen viscous mass. In the preferred suspension, thecollagen material is lightly tanned, for example to an extent comparableto l/ 10% to preferably not over 3% of combined aldehyde such asformaldehyde o-r glyoxal based on the dried weight of the skin materiaand the resulting suspension is adjusted to a pH relative to theisoelectric range of the collagen fibers of the suspension. It is notedthat according to a recent discovery certain additives appear to beeffective to allow at least some impregnation of the collagen fibersuspension even in the isoelectric range although penetration abilityfalls off sharply as the range is approached or entered. Forimpregnation, the suspension comprises preferably from about 1% to about5% by weight of fiber solids based on the weight of the suspension, andthe collagen fibers are distinct and noncolloidal with a length of fromabout 0.001 mm. to not over about 4 mm. and preferably not over about 1mm.

Because of the wide variation in properties of collagen source materialand the nature of the fibers in suspension resulting from the beatingoperation, the suspension after adjustment to a pH ordinarily eitherabove or below the isoelectric range may be calibrated for cooperationwith the combined fiber sheets to be used by filtration through a trialmat of the intermeshed fibers. In general it is preferred that therelation of the suspension and the fiber mat be such that 600 ml. of thesuspension will pass through a 6" diameter circular section in from Aminute to about 2 minutes under a vacuum of about 10" of mercury.

Penetration ability increases as the pH departs from the isoelectricrange so that a suspension having inadequate penetrationcharacteristics, for example requiring over about two minutes forpenetration may be able to be brought to a desired penetration value byadjusting its pH to a point farther removed from the isoelectric range.Conversely, a suspension having a high penetration ability andinadequate or undesirably low retention within the fiber sheet may beimproved as to these latter properties by adjusting the pH to a pointcloser to the isoelectric range. Also the rate of penetration is greaterwith lower concentrations of fibers in the suspension, and penetrationmay be improved by diluting the suspension. After adjustment of thesuspension to a pH and concentration giving a desired penetration valuefor the selected fiber mat, penetration of the mat for making of thefinal product is begun. This penetration is preferably effected by usingvacuum or pressure for forcing the suspension into the assembled fibersas supported on a screen. In this penetration step, where there are twomats, the mat presenting surface fibers parallel to the surface may beeither above or below the base sheet. That is, it may be on the side towhich the collagen fiber suspension is applied or it may be on the sideopposite that to which the collagen fiber suspension is supplied. Ineither case, the collagen fibers are caused to impregnate the assemblyof sheets to provide a substantial concentration of collagen fiberslurry at least at the interface between the two sheets and in thesections of the base sheet and second sheet adjacent the interface.Optionally, the assembly of intermeshed fiber sheets may be treated morethan one time with a collagen fiber suspension. For example, a collagenfiber suspension having good penetrating ability may be used for a firsttreatment and thereafter the assembly may be treated with a suspensionhaving a lower penetration ability. If desired the collagen fibersuspension may be applied from alternating sides.

Deswelling of the collagen fibers within the intermeshed fiber mass maybe effected by reducing the acid or alkali content of a collagen fibermaterial. This action may be secured by extracting the fibrous mass withdistilled water or with a water-miscible volatile organic solvent suchas acetone or other ketones and lower alcohols such as methanol, ethanoland isopropanol. Alternatively, the fiber base may be treated with anaqueous solution of a buffer salt such as an acetate or phosphatebuffered system to bring the pH to a value, for example in the range ofabout 3.5 to about 6, at which reaggregation of the collagen microscopicfibers will occur. Reaggregation may also be effected by treating thefiber batt with a aqueous ammonium sulfate solution which effects adeswelling of the fibers.

The fiber mat assembly is compacted and reduced in thickness in thecourse of penetration by the suspension and reaggregation of thecollagen material so that, for example, starting with a mat assemblyhaving an initial thickness of 0.19, after penetration by suspension andreaggregation of the collagen material, the thickness may have reducedto about .03. This reduction in thickness is due in considerable measureto the action of the suspension in being forced into the mat assembly. Afurther action which influences the reduction in thickness is thepulling together of the collagen material by water bonding; and thisfactor may range from very slight where water is extracted from thesheet by solvent to relatively large where a substantial portion of thewater is removed by evaporation.

The sheet material is preferably subjected to tanning with mineraltanning agents such as chrome tanning liquors or with vegetable tanningagents or with combination tanning agents. Because of the collagendeswelling action of mineral tanning agents such as chrome tanningagents it is possible to effect both reaggregation and tanning with suchagents. Conventional leather tanning procedures may be used and thetanning may be carried out either in an aqueous tanning medium or asolvent type tanning medium.

After tanning the sheet material will be washed and manually pressed toremove excess water. Ordinarily the sheet is subjected to a treatment tointroduce a plasticizing or softening agent into it as by fat liquoringor pref erably by immersing it in an acetone solution containing forexample, 4% by weight of oleic acid. After this treatment, the sheet isdried in air and may be subjected to various finishing treatmentsincluding fat liquoring, resin treatments, staking and so on.

For use, the surface of the sheet may be coated with leather finishes orresinous and/or waxy material. One finish for the sheet materialinvolves the application to the surface of the sheet of certain soluble,800 type, nylons (which are alkoxy derivatives of type 66 nylon) whichare believed to contain groups reactive with certain groups of thecollagen material. Formation of this coating may involve a deposition asby spraying of a solution of a suitable nylon in a 70% isopropanolsolution, this solution suitably containing pigment to give the desiredcolor. After the solution is applied the sheet may be dried, subjectedto a needling treatment, and thereafter embossed or plated. The surfaceso obtained is a soft, strong and flexible film closely resembling thegrain surface of leather and firmly adherent to the sheet.

The following examples are given to aid in understanding the inventionand it is to be understood that the invention is not restricted to theparticular materials or conditions set forth in the examples.

EXAMPLE I A needle loomed nonwoven 3 denier polypropylene fiber mathaving a weight of 7.5 ounces per square yard was laid up in face toface relation with a nonwoven cotton fiber mat having a weight of about2 ounces per square yard. The associated fiber mats were disposed on afilter bed provided with means for applying suctionfthe cotton fiber matbeing uppermost.

An aqueous dispersion of collagen fibers of microscopic size wasprepared by tanning hide material with formaldehyde to give aformaldehyde content of about 0.20% by weight and beating the hidematerial together with water in a beater similar to a paper beater at apH of about 5. The collagen fibers thus produced had a length of about0.2 to 1 mm. The suspension was diluted to bring the 6 solids content toabout 1% and the pH was adjusted to 3.5.

A quantity of the above-prepared fiber suspension was deposited on theassociated fiber mat on the filter bed as a layer of uniform thicknessand suction was applied to pull the suspension into the associated matfiber structure. The vacuum applied was 29 inches and after one minutethe associated fiber structure of the mat was filled with thesuspension.

The mat with collagen fiber in it was removed from the filter bed andreplaced with the cotton fiber side down. A further quantity of the samecollagen fiber suspension at pH 2.5 was deposited on the mat and pulledin by suction. Two portions of acetone were applied successively to thesheet on the filter bed and sucked through to remove water and effectreaggregation of the collagen fiber in the mat.

The resulting sheet material after removal from the filter bed andevaporation of the acetone had a collagen content of about 43.3% byweight based on the total weight of mat fibers and collagen.

The impregnated mat then was placed in a chrome tanning bath containing1% by weight chromium calculated as Cr O and 2% by weight of sodiumformate. After standing overnight in this tanning bath, the sheet wasremoved, washed in warm tap water for six hours, pressed between filterpaper to remove further water and disposed in a fat liquor bath. Afterfat liquoring the sheet was removed and air dried. The sheet resembled achrome tanned leather in which the surface on which the cotton fiber matwas disposed had a fine uniform appearance resembling a grain layer.

EXAMPLE II A needle loomed nonwoven 3 denier polypropylene fiber mathaving a weight of 6.6 ounces per square yard was laid up in face toface relation with a square woven cotton fiber cloth (Batiste) having athread count x 98. The fiber mat and the cloth were disposed on a filterbed provided with means for applying suction, the 3 denier fiber matbeing uppermost.

An aqueous disperson of collagen fibers of microscopic size was preparedby tanning hide material with formaldehyde to give a formaldehydecontent of about 0.15% and beating the hide material in a heater similarto a .paper beater. The collagen fibers thus produced had a length ofabout 0.2 to 1 mm. The suspension was diluted to bring the solidscontent to about 2% and and the pH was adjusted to 3.18.

A quantity of the above-prepared fiber suspension was deposited on theassociated fiber mat and cloth on the filter bed as a layer of uniformthickness and suction was applied to pull the suspension into theassociated mat fiber structure. The vacuum applied was 25 inches and theassociated fiber structure of the mat was filled with the suspension.

After impregnation, the impregnated associated mat was removed from thefilter bed and while still wet with water was placed in a chrome tanningbath containing 1% by weight chromium calculated as Cr O and 2% byweight of sodium formate, the bath having a pH of about 4.2. Afterstanding 6 hours in this tanning bath, the sheet was removed, washed inwarm tap water for 6 hours, pressed between sheets of filter paper toremove further water and disposed in a fat liquor bath. After fatliquoring the sheet was removed and air dried. The sheet resembled achrome tanned leather in which the surface on which the cloth wasdisposed had a fine uniform appearance resembling a grain layer.

EXAMPLE III A needle loomed nonwoven 3 denier polypropylene fiber mathaving a weight of 7.5 ounces per square yard was laid up in face toface relation with a nonwoven 1.5 denier polypropylene fiber mat havinga weight of 1.48

ounces per square yard. The associated fiber mats were disposed on afilter bed provided with means for applying suction, the 3 denier fibermat being uppermost.

An aqueous dispersion of collagen fibers of microscopic size wasprepared by tanning hide material with formaldehyde to give aformaldehyde content of about 0.2% and beating the hide material in abeater similar to a paper beater. The collagen fibers thus produced hada length of about 0.2 to 1 mm. The suspension was diluted to bring thesolids content to about 1% and the pH was adjusted to 3.34.

A quantity of the above-prepared fiber suspension was deposited on theassociated fiber mat on the filter bed as a layer of uniform thicknessand suction was applied to pull the suspension into the associated matfiber structure. The vacuum applied was 29 inches and after aboutminutes the associated fiber structure of the mat was filled with thesuspension.

After impregnation, the impregnated associated mats were removed fromthe filter bed and dehydrated by immersion in acetone. At this stage thesheet was found to have a collagen content of 47% by weight based on thecombined weight of the mat fibers and collagen fibers. The sheet wasplaced in a chrome tanning bath containing 5% by weight chromiumcalculated as Cr O and 1% by weight of sodium formate, the bath having apH of about 4.0. After standing 2 hours in this tanning bath, the sheetwas removed, drained and allowed to stand overnight. The sheet waswashed in tap water for two hours, pressed between filter paper toremove further water and disposed in a fat liquor bath. After fatliquoring the sheet was removed and air dried. The sheet resembled achrome tanned leather in which the surface on which the 1 denier fibermat was disposed had a fine uniform appearance resembling a grain layer.

EXAMPLE IV A nonwoven unneedled mat of 1 /2 denier polypropylene fiberhaving about crimps to the inch and weigh ing about 5.66 ounces persquare yard was disposed on a filter bed provided with means forapplying suction. An aqueous dispersion of collagen fibers ofmicroscopic size as in Example II was diluted to bring the solidscontent to about 2% and the pH was adjusted to about 3.2. A quantity ofthe fiber suspension was deposited on the fiber mat and suction wasapplied to pull the suspension into the mat fiber structure.

After impregnation, the impregnated mat was treated while on the filterbed with a chrome tanning bath containing 1% by weight chromiumcalculated as Cr O and 2% by Weight of sodium formate, the bath having apH of about 4.2. After the treatment of the mat with the tanning agent,the sheet was allowed to stand overnight, removed from the filter bed,washed in warm tap water for six hours and thereafter fat liquored anddried. The sheet had properties comparable to a chrome tanned leathermaterial and had a fine uniform appearance resistant to the developmentof surface irregularities when stripped, On analysis it was found thatthe product had about a 65% collagen content based on the combinedweight of polypropylene fiber and collagen fiber.

EXAMPLE V A needle loomed nonwoven 3 denier polypropylene fiber mathaving a Weight of about 7 ounces per square yard was disposed on afilter bed provided with means for applying suction. On the exposed faceof this fiber mat there was laid a mat of unneedled 4.6 denier nylonuncrimped fiber having a weight of about 1 ounce per square yard. An 80mesh polypropylene fiber screen was disposed over the surface of theunneedled mat and a quantity of the fiber suspension described inExample IV was deposited on the surface of the screen covering theassociated fiber mats on the filter bed. Suction was applied to pull thesuspension into the associated mat fiber structure.

After impregnation, dried acetone was supplied to the surface of the matin successive portions to dry the mat. At this stage the sheet was foundto have a collagen content of 50% by weight based on the combined weightof the mat fibers and collagen fibers. The associated mat and screenwere removed from the filter bed and placed in a chrome tanning bathcontaining 1% by weight chrome calculated as Cr O and 2% by weight ofsodium formate, the bath having a pH of about 4.2. The polypropylenescreen was stripped from the sheet and the sheet allowed to standovernight in the tanning bath. Thereafter, the sheet was removed, washedin warm tap water for six hours, pressed between sheets of filter paperto remove further water and disposed in a fat liquor bath. After fatliquoring the sheet was removed and air dried. The sheet had propertiescomparable to a chrome tanned leather and was resistant to thedevelopment of surface irregularities on the surface corresponding tothe unneedled fiber layer.

EXAMPLE VI An unneedled nonwoven 2.3 denier uncrimped nylon fiber mathaving a weight of 1 oz. per square yard was laid up in face to facerelation with an unneedled mat of a blend of 3 denier high crimp nylonfiber and 3 denier polypropylene fiber, the fibers being employed in theratio of 70 parts by weight of nylon to 30 parts by weight ofpolypropylene and the mat having a weight of about 4 ounces per squareyard. The associated fiber mats were disposed on a filter bed providedwith means for applying suction with the 1 ounce per square yard matuppermost; and an mesh polypropylene fiber screen was disposed over theexposed surface of the associated mats.

An aqueous dispersion of collagen fibers of microscopic size wasprepared by tanning hide materal with formaldehyde to give aformaldehyde content of about 0.4% by weight and beating the hidematerial together with Water in a beater similar to a paper beater at apH of about 5. The collagen fibers thus produced had a length of fromabout 0.2 to about 1 mm. The suspension was diluted to a solids contentof about 1% and the pH was adjusted by addition of sulfuric acid toabout 2.6.

A quantity of the fiber suspension was deposited on the screen-coveredsurface of the fiber mats and suction was applied to pull the suspensioninto the associated mat fiber structure.

After impregnation, dried acetone was supplied to the surface of the matin successive portions to dry the mat. At this stage the sheet was foundto have a collagen content of 52% by weight based on the combined weightof the mat fibers and collagen fibers. The associated mat and screenwere removed from the filter bed and tanned as in Example V, thepolypropylene screen being stripped from the sheet. Thereafter, thesheet was removed from the tanning bath, washed in warm tap water forsix hours, pressed to remove further water and disposed in a fat liquorbath. After fat liquoring the sheet was removed and air dried. The sheethad properties comparable to a chrome tanned leather and was resistantto the development of surface irregularities when stretched.

Having thus described my invention, what I claim as new and desire tosecure by Letters Patent of the United States is:

1. The process of forming a strong fibrous sheet material whichcomprises the steps of providing a primary mat of intermeshed fibersdisposing a second mat of intermeshed fibers on a surface of saidprimary intermeshed mat, penetrating the thickness of both of said matsof intermeshed fibers with an aqueous suspension of distinct swollencollagen fibers of microscopic size and removing the swelling water fromsaid collagen to reaggregate said collagen fibers into a larger collagenfiber structure holding said primary mat of fibers and said second matof fibers firmly together in face to face relation and reinforcing theintermeshed fibers in each of said mats against displacement.

2. The process of forming a strong fibrous sheet material whichcomprises the steps of providing a primary mat of intermeshed fibers,disposing a second mat of intermeshed fibers on a surface of saidprimary mat, the fibers of said second mat at least at and adjacent thefree surface of said mat being arranged substantially parallel to saidfree surface and oriented to resist lengthwise and widthwise forcesexerted on said mat, penetrating the thickness of both of said mats ofintermeshed fibers with an aqueous suspension of distinct swollencollagen fibers of microscopic size and removing the swelling water fromsaid collagen to reaggregate said collagen fibers into a larger collagenfiber structure holding said primary mat of fibers and said second matof fibers firmly together in face to face relation and reinforcing theintermeshed fibers in each of said mats against displacement.

3. The process of forming a strong fibrous sheet material whichcomprises the steps of providing a primary mat of intermeshed textilefibers, disposing a layer of interwoven textile fibers on a surface ofsaid primary intermeshed mat, penetrating the thickness of both saidprimary mat and said layer of interwoven fibers with an aqueoussuspension of distinct swollen collagen fibers of microscopic size andremoving the swelling water from said collagen to reaggregate saidcollagen fibers into a larger collagen fiber structure holding saidprimary mat of fibers and said layer of interwoven fibers firmlytogether in face to face relation and reinforcing the fibers in each ofsaid mats against displacement.

4. The process of forming a strong fibrous sheet material whichcomprises the steps of providing a primary mat of intermeshed textilefibers of from 1 to denier, said fibers being crimped at least to theextent of about 5 crimps per linear inch and said mat beingsubstantially free from textile fibers and portions of textile fibersoriented normal to the surface of said mat, but being oriented to resistlengthwise and widthwise forces exerted on said mat, disposing a secondmat of intermeshed textile fibers of from 0.5 to 3 denier on the surfaceof said primary mat, the fibers of said second mat at least at andadjacent the free surface of said mat being arranged substantiallyparallel to said free surface and oriented to resist lengthwise andwidthwise forces exerted on said mat, said second mat beingsubstantially free from fibers and portions of fibers oriented normal tothe surface of said mat, penetrating the thickness of both of said matsof intermeshed fibers with an aqueous suspension containing from about1% to about 5% by weight of distinct swollen collagen fibers ofmicroscopic size, said collagen fibers having a content of combinedformaldehyde of from about 0.1% to about 3.0% based on the dry weight ofsaid fibers, said collagen fiber suspension being caused to penetratesaid mats in quantity sufficient to associate with said mat at leastabout 50% of collagen by weight based on the combined weight of thecollagen and mat fibers, and removing the swelling Water from saidcollagen to reaggregate said collagen fibers into a larger collagenfiber structure holding said primary mat of fibers and said second matof fibers firmly together in face to face relation and reinforcing theintermeshed fibers in each of said mats against displacement.

5. The process of forming a strong fibrous sheet which comprises thesteps of providing a primary mat of intermeshed fibers of from 1 to 5denier, said fibers being crimped at least to the extent of about 5crimps per linear inch and said mat being substantially free from fibersand portions of fibers oriented normal to the surface of said mat, butbeing oriented to resist lengthwise and widthwise forces exerted on saidmat, disposing a layer of interwoven textile fibers on a surface of saidintermeshed mat, penetrating the thickness of said primary mat and saidlayer of interwoven textile fibers with an aqueous suspension ofdistinct swollen collagen fibers of microscopic size and removing theswelling water from said collagen to reaggregate said collagen fibersinto a larger collagen fiber structure holding said primary mat offibers and said layer of fibers firmly together in face to face relationand reinforcing the intermeshed fibers in said mat and layer againstdisplacement.

6. The process of forming a strong fibrous sheet which comprises thesteps of providing a primary mat of intermeshed fibers of from 1 to 5denier, said fibers being crimped at least to the extent of about 5crimps per linear inch and said mat being substantially free from fibersand portions of fibers oriented normal to the surface of said mat, butbeing oriented to resist lengthwise and widthwise forces exerted on saidmat, disposing a layer of interwoven textile fibers on a surface of saidintermeshed mat, penetrating the thickness of said primary mat and saidlayer of interwoven textile fibers with an aqueous suspension containingfrom about 1% to about 5% by weight of distinct swollen collagen fibersof microscopic size, said collagen fibers having a content of combinedformaldehyde from about 0.1% to about 3.0% based on the dry weight ofsaid fibers, said collagen fiber suspension being caused to penetratesaid mat and said layer in quantity sufiicient to associate with saidmat and layer at least about 50% of collagen by weight based on thecombined weight of the collagen and the fibers of said mat and layer,and removing the swelling water from said collagen to reaggregate saidcollagen fibers into a larger collagen fiber structure holding saidprimary mat of fibers and said layer of fibers firmly together in faceto face relation and reinforcing the intermeshed fibers in said mat andlayer against displacement.

7. A strong fibrous sheet material which comprises a primary mat ofintermeshed textile fibers, a second mat of intermeshed textile fiberson a surface of said primary mat and a collagen fiber structureextending through the thickness of both of said mats of intermeshedfibers holding said primary mat of fibers and said second mat of fibersfirmly together in face to face relation and reinforcing the intermeshedfibers in each of said mats against displacement.

8. A strong fibrous sheet material comprising a primary mat ofintermeshed fibers, a second mat of intermeshed fibers on a surface ofsaid primary mat, the fibers of said second mat at least at and adjacentthe free surface of said mat being arranged substantially parallel tosaid free surface and oriented to resist lengthwise and widthwise forcesexerted on said mat and a collagen fiber structure extending through thethickness of both of said mats of intermeshed fibers holding saidprimary mat of fibers and said second mat of fibers firmly together inface to face relation and reinforcing the intermeshed fibers in each ofsaid mats against displacement.

9. A strong fibrous sheet material which comprises a primary mat ofintermeshed textile fibers of from 1 to 5 denier, said fibers beingcrimped at least to the extent of about 5 crimps per linear inch andsaid mat being substantially free from textile fibers and portions oftextile fibers oriented normal to the surface of said mat, but beingoriented to resist lengthwise and widthwise forces exerted on said mat,a second mat of intermeshed textile fibers of from 0.5 to 3 denier on asurface of said primary mat, the fibers of said second mat at least atand adjacent the free surface of said mat being arranged substantiallyparallel to said free surface and oriented to resist lengthwise andwidthwise forces exerted on said mat, and a collagen fiber structureextending through the thickness of both of said mats of intermeshedfibers holding said primary mat of fibers and said second mat of fibersfirmly together in face to face relation and reinforcing the intermeshedfibers in each of said mats against displacement.

10. A strong fibrous sheet material which comprises a primary mat ofintermeshed textile fibers of from 1 to 5 11 12 denier, said fibersbeing crimped at least to the extent References Cited of about 5 crimpsper linear inch and said mat being UNITED STATES PATENTS substantiallyfree from fibers and aoruons of fibers 2,802,767 8/1957 Mightonlorlented normal to the surface of sa1d mat, but being 2908 O6 4 10/1959Lauterback et a1 28 72 oriented to resist lengthwise and widthwiseforces exerted 5 3:223:551 12/1965 Tu on said mat, a layer of interwoventextile fibers on a surface of said primary intermeshed mat holding saidROBERT F. BURNETT, Primary Examiner.

primary mat of fibers and said layer of interwoven textile WILLIAMPOWELL, Assistant Examiner.

fibers firmly together in face to face relation and reinl0 forcing theintermeshed fibers in said mat and layer US. Cl. X.R.

against displacement 161-81, s2, 88, 154, 155, 156, 59; 117-440; 156148

